Battery Monitor vs Voltage

[Kapena]

As with nearly every post about electricity...the number of incorrect posts exceeds the number of correct ones.

At 8 amps your battery is fully charged for 460AH system. Voltage is a poor indication of charge level on a battery, that is why you use a battery monitor. Under charge the voltage will rise to 14.2 volts, at rest somewhere between 12.2 to 12.8 volts, discharged voltage must remain above 10.8 volts for damage not to occur. At 33 AH discharged you are 14% discharged...you only get to take out a total of 230 AH, 1/2 the capacity. If you remove the 230 AH you have to pump 460 AH back into the batteries to charge them fully...That is the way it works.

So only thing wrong is that your monitor is not correcting for the 50% maximum discharge. This is most likely a setting. Nothing wrong or incorrect in the voltage reading as it does not indicate charge status very well. It is normal for the voltage to sag when some current is drawn from the batteries.

[btrayfors]

Defjef,

The reason for checking voltage at the battery terminals with a digital multimeter is to verify, independently and with a known good instrument, that what you are seeing on the monitor is accurate.

While your connections may be clean and tight, and the monitor may be reading correctly, it's not always the case. I've seen several cases on client's boats where the monitor does not accurately reflect the battery voltage.

And, yes, measuring at the terminals of a battery is just as accurate, providing that you apply the probes correctly. The amperage required to drive a very high impedence digital multimeter is miniscule, so it doesn't take much effort to get a good reading.

Final point: in a battery bank consisting of four 6-volt golf cart batteries -- such as the OP has -- how are you going to measure the individual voltages of each battery unless you test each at their terminals?

Bill

[btrayfors]

Originally Posted by Kapena

As with nearly every post about electricity...the number of incorrect posts exceeds the number of correct ones.

At 8 amps your battery is fully charged for 460AH system. Voltage is a poor indication of charge level on a battery, that is why you use a battery monitor. Under charge the voltage will rise to 14.2 volts, at rest somewhere between 12.2 to 12.8 volts, discharged voltage must remain above 10.8 volts for damage not to occur. At 33 AH discharged you are 14% discharged...you only get to take out a total of 230 AH, 1/2 the capacity. If you remove the 230 AH you have to pump 460 AH back into the batteries to charge them fully...That is the way it works.

So only thing wrong is that your monitor is not correcting for the 50% maximum discharge. This is most likely a setting. Nothing wrong or incorrect in the voltage reading as it does not indicate charge status very well. It is normal for the voltage to sag when some current is drawn from the batteries.

I certainly agree with the first sentence. However, the rest of the post is...well...misleading at best and mostly just plain wrong.

Example: If you remove 230AH from the battery bank you do NOT have to "pump 460AH back into the batteries to charge them fully". You have to put back the 230AH plus about 10-20% extra to make up for losses in the charging process.

Bill

[Kapena]

BT...another wrong post...look it up, then apologize.

Lead-acid deep cycle.

[Cruisin Cat]

Don,

I have a Victron battery monitor also and it works well. I check it against the battery voltage (after resting) from time to time and get good agreement.

The common problems which cause battery monitors to show incorrect SOC are:

1. The current threshold to recognise 100% SOC is set too low. In your case using the factory preset 4% will result in the monitor assuming 100% SOC when that is not yet reached. I suggest you go into the Setup menu and reduce the setup parameter called "It" to 0.5% or at least to 1%.

Other setup parameters that effect detection of 100% SOC are:
"Vc" - factory preset is 13.2V (on my Victron) which is way too low. I suggest you set to 14V - 14.2V (I don't remember what type of batteries you have but this setting should work for most types)
"Tcd" which I suggest you set to around 5 min (not so critical)

2. The primary source of information that the battery monitor uses to determine SOC is the current going in and out of the batteries and that is measured by a shunt in the cable going to the negative terminal of your battery bank. This shunt should be very close to the negative battery terminal and most importantly, nothing should be connected to negative between the shunt and the batteries. If there is more than 1 battery bank, this applies to all battery bank negative connections....a cable must be run from each battery bank negative terminal and all joined at the shunt. This must be the only connection to negatibe on the battery side of the shunt. All power consuming and/or generating equipment must be connected to negative on the load side of the shunt.

Sometimes (as happened on my boat) a previous owner or equipment installer will install new equipment and connect the negative side directly to the negative terminal of a battery bank....which bypasses the shunt and hence any power that new equipment uses is not detected by the battery monitor and so the battery monitor will show higher SOC than actual (assuming this new equipment is a power consuming device....if it is a power generating device SOC will show lower than actual).

This is more common when the boat has more than 1 battery bank separated by some distance and it seems to the installer much easier to connect the negative of the new equipment to the negative of the adjacent battery bank rather than run a cable all the way back to the shunt adjacent to the other battery bank.

3. Battery charging system(s) voltage is not set to correct voltage for the the type of batteries employed....eg, on my cat I have 2 x Volvo D130f engines both with 110A altinators and internal regulators. Right out of the factory one of these altinators charges at 14.2V and the other charges at 13.8V...and Volvo says this is within specification! Obviously I'm never going to reach 100% SOC if I'm running the 13.8 V altinator.

Hope this helps and happy to answer any other questions you might have about the Victron

[kiltym]

Originally Posted by Stu Jackson

"Breaking In" New Wet Cell Batteries

Link-series Charging Algorithms -- The "Gotcha" Factor!

Thanks for posting these links, both have good information.

I do however have a question on something written about the Link Series Gotcha, as I have 6 new batteries, a Link 1000, a Freedom 15 Invert/Charger and am trying to make sure I have things sorted as I also see lower voltage then I would expect on my new batteries. I am going to drain them down low and see how many AH I actually get out of them, a few times like "breaking-in" describes.

Back to my question.

You stated:
"The scenario for the Link 20 gotcha is this: The charging current has tapered down to about 13A with 20Ah still to go with the charging voltage at 14.4V. Now one of the refrigeration units turns on drawing 5A. This causes the battery charge current to drop below the 2% threshold and after 6 minutes the Link 20 thinks the batteries are fully charged because the charge voltage is over 13.2V, the charge current is below 2% or 9.2A, and these conditions have been met for 6 minutes."

I 100% understand what you are saying, except two things. If my charger is putting in 14.4V, its either in bulk or accept. Lets say its in accept. Its a 75Amp charger, say at the moment, putting in 13amps.

If my fridge turns on, the charger needs/wants to maintain the voltage at 14.4. At the moment, it needs a +13Amp load to do that. So, if my fridge turns on (lets say 5amps) all that I think happens is the charger now puts out 18Amps to keep the net at 13amps to maintain the 14.4V. So I don't think what you state above is correct, but I am asking since I might be missing something. I don't think the fridge turning on will cause the Link to go into Float mode prematurely (or reset the Link to 100% full).

Changing the 2% threshold to 1% makes sense. But changing the 13.2 float cutoff to 15V also does not make sense to me.

Since the Link controls the Freedom Charger, in this case, the charger will NEVER enter float mode and you will eventually be overcharging your batteries at 14.4V.... Again, am I missing something? Seems like a bad idea to me.


And, I have a MC612 regulator on my alternator, and I am trying to get that "correct" also. There are 2 charge efficiency parameters with a default setting of 78%. This is used to move the regulator from bulk-accept-float. Does anyone know if 78% is a good number, or how can I determine a better number to use to make sure the batteries are really getting full?

Thanks for your help in understanding all this as I want to make sure the monitor is setup as correctly as possible.

[Stu Jackson]

If my fridge turns on, the charger needs/wants to maintain the voltage at 14.4. At the moment, it needs a +13Amp load to do that. So, if my fridge turns on (lets say 5amps) all that I think happens is the charger now puts out 18Amps to keep the net at 13amps to maintain the 14.4V. So I don't think what you state above is correct, but I am asking since I might be missing something. I don't think the fridge turning on will cause the Link to go into Float mode prematurely (or reset the Link to 100% full).

Mark, Good question, thanks for asking.

Cruisin' Cat answered this in Reply #20 above, in a much shorter and succinct manner than my long rambling Gotcha post.

The issue is having the Link show full PREMATURELY and flipping the Freedom to float too soon.

In your example, you seem to imply that your charger will increase its amperage to make up for the run of the fridge. That just doesn't happen, 'cuz neither the charger nor the Link know that all of a sudden the fridge starts, other than having the net amperage be reduced to below the default 2%, which is the whole reason to change the DEFAULT parameters.

The charger is working based on the acceptance of the battery bank. That doesn't change (albeit very much) when your fridge starts when you're in absorption mode.

The Link, as noted, is only reading the NET current, so when the fridge kicks in, as discussed many times in my Gotcha link, the simple math reduces the amperage by reading net amps, and prematurely kicks the Freedom into float via the Link. That's why changing the default parameters is so important.

The fridge is working off the batteries, but by that time in the charge cycle (absorption) the charger does NOT increase its charge amperage because something turned on. The voltage has reached its setpoint, and the amperage is being controlled by the battery acceptance, NOT the load on the system.

Also, since I have seen it happen, your last sentence doesn't apply (I don't think the fridge turning on will cause the Link to go into Float mode prematurely (or reset the Link to 100% full).) With all due respect, you are incorrect and it certainly does. That was the reason for the entire topic.

I think you are misunderstanding the charging regimen. Chargers don't "think/need/want" to put more amperage in because a load is present. By the time the 85% or so SOC is reached, and the amperage from your 75A charger is down to 13A, you are filling that hard to do last 10 or 15% of the charge cycle. The Link reads net current and acts accordingly. Battery acceptance determines (or limits - i.e., it "pushes back" against the charger's total amperage) the current "allowed" to go back into the batteries.

Changing the 2% threshold to 1% makes sense. But changing the 13.2 float cutoff to 15V also does not make sense to me.

Since the Link controls the Freedom Charger, in this case, the charger will NEVER enter float mode and you will eventually be overcharging your batteries at 14.4V.... Again, am I missing something? Seems like a bad idea to me.

Yes, I think you are missing something. First, I've seen it happen. Second, the issue, as discussed in my Gotcha link, is that the ONLY issue is to avoid the change PREMATURELY, not ever. You might want to go back and re-read the Gotcha link, because someone asked the very same question and it was asked and answered. It's in Reply #3, here: Link-series Charging Algorithms -- The "Gotcha" Factor!

Think of it this way: You're concerned that the 14.4V will be on too long. My concern, and the reason for changing the defaults, is that the lower float voltage will start too soon!

The charger WILL enter float, but NOT prematurely. Again, as I noted, I have seen it happen. You will NOT overcharge your batteries. You WILL, however, extend the absorption stage, hasten the full charge and avoid going to float prematurely.

Hope this helps.

Note: Edited a number of times since original posting

[kiltym]

First, thanks for spending the time to get back to me.

I still have a question or two .

Originally Posted by Stu Jackson

In your example, you seem to imply that your charger will increase its amperage to make up for the run of the fridge. That just doesn't happen, 'cuz neither the charger nor the Link know that all of a sudden the fridge starts, other than having the net amperage be reduced to below the default 2%, which is the whole reason to change the DEFAULT parameters.

So this is how I understand it, but if I am wrong, thats ok .

In the acceptance/absorption stage, the charger reduces its amps accordingly to keep the voltage at a constant, say 14.4V.

The more the batteries are charged, the charger is able to reduce the amps.

Is this correct?

If so, then what logically makes sense to me is that if the charger needs to apply 13amps of power to keep the 14.4V, if the fridge cycles on, all of a sudden the amps go down to 7, but the voltage at the batteries will also drop because of the less amps, say to 14.2 or so. The charger will see the voltage drop, and increase the amps again to get the voltage back up to the 14.4V that it wants to maintain during this phase, which will mean more amps from the charger and in turn the same "net" of +13 amps again, and the voltage goes back to 14.4.

I guess I am still not understanding something.....?

Originally Posted by Stu Jackson

The Link, as noted, is only reading the NET current, so when the fridge kicks in, as discussed many times in my Gotcha link, the simple math reduces the amperage by reading net amps, and prematurely kicks the Freedom into float via the Link. That's why changing the default parameters is so important.

I get the math, I just don't get my question above and why the charger doesn't have to increase amps again to keep voltage at the correct level.

Originally Posted by Stu Jackson

The fridge is working off the batteries, but by that time in the charge cycle (absorption) the charger does NOT increase its charge amperage because something turned on. The voltage has reached its setpoint, and the amperage is being controlled by the battery acceptance, NOT the load on the system.

OK, so maybe this is where I dont understand something. I assume the charger will increase amperage to keep the voltage constant..... But you imply this is not the case?

Originally Posted by Stu Jackson

I think you are misunderstanding the charging regimen. Chargers don't "think/need/want" to put more amperage in because a load is present. By the time the 85% or so SOC is reached, and the amperage from your 75A charger is down to 13A, you are filling that hard to do last 10 or 15% of the charge cycle. The Link reads net current and acts accordingly. Battery acceptance determines (or limits - i.e., it "pushes back" against the charger's total amperage) the current "allowed" to go back into the batteries.

Perhaps I am misunderstanding this. Everything I read (which might be wrong ), implies that the charger pulls back on the amp load to keep voltage constant during acceptance phase. You imply that the charger is still working just as hard but is only able to put in a lower amp at 85%SOC because the batteries are "pushing back". But, this doesn't make sense to me as I know the charger/alternator are working less as the batteries get charged during this phase and the amps are lowered. The easiest place to notice is the load on the engine is much less as the amps lower during this phase.

Something still doesn't make sense to me.

Originally Posted by Stu Jackson

Since the Link controls the Freedom Charger, in this case, the charger will NEVER enter float mode and you will eventually be overcharging your batteries at 14.4V.... Again, am I missing something? Seems like a bad idea to me.

Yes, I think you are missing something. First, I've seen it happen. Second, the issue, as discussed in my Gotcha link, is that the ONLY issue is to avoid the change PREMATURELY, not ever. You might want to go back and re-read the Gotcha link, because someone asked the very same question and it was asked and answered. The charger WILL enter float, but NOT prematurely. Again, as I noted, I have seen it happen. You will NOT overcharge your batteries. You WILL, however, extend the absorption stage, hasten the full charge and avoid going to float prematurely.
Hope this helps.

So, how does the Freedom go into Float mode if the parameters are set at 1% and 15V. There is no way this will ever be met....? I have read that post a few times and I still am not understanding, sorry. What causes the charger to enter float mode?

Thanks for your time on this, I am sure its appreciated by more then just me....

[Stu Jackson]

Mark,

This system doesn't allow changes after 30 minutes of the original posting (not such a great idea), but here are some furhter thoughts.

If my fridge turns on, the charger needs/wants to maintain the voltage at 14.4. At the moment, it needs a +13Amp load to do that.

It doesn't NEED a 13A load to do that. Voltage for bulk are usually, if not always, simply set by time on chargers, including external regulators. RTFM. So, you're charger is putting out 14.4V in bulk and absorption stages, but the amperage has been reduced down to 13A. This is because of battery acceptance, nothing from the charger's end.

That's how it works.

Your post came in after I started this.

In the acceptance/absorption stage, the charger reduces its amps accordingly to keep the voltage at a constant, say 14.4V.

You have it backwards. The voltage starts out with a GOAL of, say, 14.4V, with as much current as the batteries can handle (acceptance), and the voltage rises as the bank gets charged. Once the voltage gets to its setpoint, it stops rising, and the current is determined by the SOC of the bank, and its acceptance (ability to accept charge).

I haven't gone into the rest of your questions in more details, since they are pretty well covered in the Freedom manual and any other 3 stage charging explanation.

It's all about battery acceptance.

So, how does the Freedom go into Float mode if the parameters are set at 1% and 15V. There is no way this will ever be met....? I have read that post a few times and I still am not understanding, sorry. What causes the charger to enter float mode?

Please re-read the Gotcha topic, really, it's all there, especially in the second link I just gave you, Reply #3. The simple answer is the difference between PREMATURELY and really FULL.

It will show full when the ah counter gets to zero, it just won't do it prematurely based on those other parameters, which are factory set defaults, which are made to be changed. Do the math.

Reply #3 states: "He's NOT saying it never will say full, he's saying that it will NOT show a "full" display PREMATURELY based on the recognition of the 2% and 132.V"matching" for 4 minutes (regardless of what the amp hour/kWhr counter is doing) and will not say full until the ah are counted down to zero."

That's when it goes into float.

1. implies that the charger pulls back on the amp load to keep voltage constant during acceptance phase. You imply that the charger is still working just as hard but is only able to put in a lower amp at 85%SOC because the batteries are "pushing back".

2. But, this doesn't make sense to me as I know the charger/alternator are working less as the batteries get charged during this phase and the amps are lowered. The easiest place to notice is the load on the engine is much less as the amps lower during this phase.

1. No, the charger doesn't pull back to keep the voltage constant. The voltage rises as does the amperage. Watch your meter on a discharged bank when it starts charging. Both rise, until the voltage setpoint is reached. Amperage can still rise, but eventually starts dropping based on the acceptance.

2. Yes, but see #1.

Stu

[Stu Jackson]

Time limit, new post again.

Mark, going into float is NOT full, it is simply the last stage of charging. Going into float prematurely lengthens the time to charge, 'cuz float voltage is lower than bulk or absorption voltage.

I'd be glad to keep this going, but suggest you try the Gotcha topic a few more times, since you're not the only one to have this issue.

The issue is DEFAULT parameters that simply do not work in real life with 400 ah banks and fridges, as demonstrated in the topic, which was initiated by another boater, not me, and by the post by Cruisin' Cat above. FYI, we had this same discussion on the ybw forum (UK) and others.

Stu

[btrayfors]

Stu, Maine, et. al...

I believe the interaction between the batteries being charged, the charger, and the applied loads during charging is somewhat more complex than implied here. This is based, inter alia, on some simple tests using three different battery chargers, differential loads, and two banks of gelled and flooded golf cart batteries which I happen to have in my shop within easy reach at the moment.

I used a variable resistive load consisting of six 12-volt light bulbs of different wattages on a board, allowing me to screw in the desired load from about 2A to 13A.

The first two tests were on the gelled golf-carts...about 220AH capacity. For the first tests I used an old Heart inverter/charger which has multiple stages and variable finishing voltage. Here's what I found:

The gels were in an almost charged state. When I applied the charger, I measured 43A @ about 13.9 volts (no load). When I switched in the light-bulb loads I saw virtually no change in the amperage put out by the charger....it varied only by 1 or 2 amps, no matter the size of the load. In other words, the amperage increased from 43A to about 44A or 45A maximum with loads from 2A to 13A.

Later, when the acceptance amperage had dropped to around 25 to 30, I applied the 13A load several times and only saw an increase of 3 or 4 amps.

This tends to support Stu's belief, at least in part.

I then applied a 10A Guest portable charger to the same gelled bank. At 13.6 volts charging, the applied 13A load only bumped the charging amperage up by 0.9A.

Clearly, the load was being furnished by the batteries and the acceptance as seen by the charger only changed a bit.

The third test was with a T-105 flooded bank (225AH) which was at a 100% state-of-charge, but in poor condition (less than 40% of original capacity remaining). The charger was an Iota DLS-45/IQ4, and the results were very different from the other chargers.

With a starting float voltage of 13.8 and with 0.6A being delivered to the batteries, when I applied the 13A light-bulb load the Iota jumped from 0.6A output to 14.6A output, and the voltage dropped from 13.8 to 13.4. Clearly, then, the Iota was attempting to keep up with the load and increased its output by 14A in order to do so. Probably, because the T-105s were in poor health it put out more than it otherwise might have had better batteries been tested.

I saw no evidence whatsoever that the application of these loads...up to 13A as tested...resulted in any change in the stage of charging...bulkabsorption/float. The gels started off in the absorption mode and remained so. The Iota started off in the float mode and remained so. Same thing with the Victron Multi-Plus on my boat, attached to a bank of 6 T-105s. It tends to remain in the same stage even as loads such as lights, bilge pump, fresh water pump, frig, etc. are turned on and off.

While these simple tests are far from scientific and definitive, I believe we can nevertheless draw a couple of tentative conclusions from them:

1. Indeed, there is an interaction between applied loads while charging and the output of the charger; and

2. The magnitude of the change in output from the charger will depend on a number of factors, including the design of the charger circuitry itself, the size and duration of the applied load(s), the state of health of the battery bank and it's total capacity and, no doubt some other factors not yet discovered or described.

Not all battery chargers are created equal....they vary considerably in their internal circuitry and their logic.

FWIW,

Bill

[kiltym]

Originally Posted by Stu Jackson

If my fridge turns on, the charger needs/wants to maintain the voltage at 14.4. At the moment, it needs a +13Amp load to do that.

It doesn't NEED a 13A load to do that. Voltage for bulk are usually, if not always, simply set by time on chargers, including external regulators. RTFM. So, you're charger is putting out 14.4V in bulk and absorption stages, but the amperage has been reduced down to 13A. This is because of battery acceptance, nothing from the charger's end.

OK, so the charger is trying to maintain a constant voltage on the batteries. So if there is a draw on the batteries of 5amps, wont the batteries in turn also be able to simultaneously accept those 5amps by the charger?

Originally Posted by Stu Jackson

It will show full when the ah counter gets to zero, it just won't do it prematurely based on those other parameters, which are factory set defaults, which are made to be changed. Do the math.

Just to make sure we don't mix things, there are 2 separate items being talked about:

1) The Link's ability to report "FULL".

2) The ability for the Freedom Charger to go into Float Mode

Originally Posted by Stu Jackson

Reply #3 states: "He's NOT saying it never will say full, he's saying that it will NOT show a "full" display PREMATURELY based on the recognition of the 2% and 132.V"matching" for 4 minutes (regardless of what the amp hour/kWhr counter is doing) and will not say full until the ah are counted down to zero."

That's when it goes into float.

So you are telling me that the charger is going to float when aH reads 0 on the link monitor? Ill have to try it myself to believe it. But if thats the case, that's great and make a lot more sense to me.

[Stu Jackson]

If so, then what logically makes sense to me is that if the charger needs to apply 13amps of power to keep the 14.4V, if the fridge cycles on, all of a sudden the amps go down to 7, but the voltage at the batteries will also drop because of the less amps, say to 14.2 or so. The charger will see the voltage drop, and increase the amps again to get the voltage back up to the 14.4V that it wants to maintain during this phase, which will mean more amps from the charger and in turn the same "net" of +13 amps again, and the voltage goes back to 14.4.

Nope. When you're plugged in, the voltage, once it reaches that 14.4V will STAY there since the shorepower is available. Voltage will only sag when there's no charging source present.

Chargers just aren't that smart, at least not as smart as you're giving them credit for!

The charger doesn't know anything about "increasing amps to get back to voltage." They provide rising voltage to a setpoint, but usually if not always governed by time in the bulk stage.

What you state simply doesn't happen.

Stu

[kiltym]

Originally Posted by Stu Jackson

Mark, going into float is NOT full, it is simply the last stage of charging. Going into float prematurely lengthens the time to charge, 'cuz float voltage is lower than bulk or absorption voltage.

I know this. But, something has to trigger the Freedom to go into Float mode. What is this trigger?

And I am happy to keep the acceptance phase going longer as I agree this makes sense, but I want to understand what is eventually going to make the charger go into float mode and reduce the voltage so I don't boil off all my liquid.

You stated before its when aH is 0. In the Freedom manual it states its on a 1hour timer, but, this timer is not valid if the charger is attached to a Link battery monitor. But, it doesn't then say what the "trigger" is..... Just says read the Link manual, but there is nothing in there..... I do RTFM all day long, and then come here .

[Stu Jackson]

So, you are telling me that the charger is going to float when aH reads 0 on the link monitor? Ill have to try it myself to believe it. But if thats the case, that's great and make a lot more sense to me.

Good. WADR, thast's exactly what I've written about in the Gotcha topic. I have tested it and seen it happen. What happens when you change the parameters, that after a daysail the almost immediate trip from bulk to absorption to float with the fridge on doesn't happen anymore. It goes bulk to absorption quickly, but doesn't trip right away to float.